This invention is directed to a pressure relief arrangement for a fluid actuator, and, more particularly, is directed to such a pressure relief arrangement for a linear fluid actuator that converts a thermal input to a mechanical output.
Electro-thermal actuators and other fluid actuator devices that restrain a fluid pressure by means of a rolling diaphragm are sometimes subject to pressures great enough to cause violent disassociation of the parts constituting the actuator. In a thermal actuator, such a high pressure might occur if the unit were heated well beyond normal operating conditions, for example, by a fire occurring in the building in which the actuator were located. Moreover, in those electrothermal actuators normally energized for short intervals, a prolonged energization of the same might effect such an undesirable large pressure build up. Thus, abnormal excessive pressure build up may be due to external ambient or overload conditions of the actuator, excesssive energization input, etc.
The present invention which provides relief of excessive pressures in a fluid actuator device without violent disassociation of the parts thereof, will be described in detail herein with reference to an electro-thermal linear fluid actuator device or thermal actuator, as shown, for example, in U.S. Pat. Nos. 3,609,635 and 3,805,528. Such a thermal actuator includes a main body or casing and an extensible member, such as a diaphragm in sealed engagement with the body to define a fluid chamber having a volume that is variable according to the position of the extensible member with respect to the body. By heating a thermally expansive working medium in the chamber, the pressure therein is increased and tends to urge the extensible member away from the body expanding the chamber and performing mechanical work. It is to be understood, however, that the principles of the invention may be applied to other types of fluid actuator devices, especially linear fluid actuator devices, such as those that operate in response to a pneumatic or hydraulic fluid input to the chamber.